1. Field of the Invention
The present invention concerns a method for suppressing at least one acoustic interference signal by using a directional microphone system that has at least two microphones, and to an apparatus for implementing the method.
2. Description of the Prior Art
The matching of microphones in a directional microphone system is of significant importance for the suppression of interference signals.
In the case of steady-state matching, the microphones in a directional microphone system are matched to one another in the steady state in open air. This matching process is generally carried out using a measurement device that allows amplitude matching and phase matching of the individual, generally omnidirectional, microphones to be carried out. Steady-state matching allows a diffuse interference sound field to be eliminated from the directional microphone signal. Matching which is carried out in open air, however, is partially corrupted again by the influence of the head on the sound propagation during operation of a directional microphone system which is used, for example, in a hearing aid.
Additionally or alternatively, adaptive amplitude and phase matching algorithms have been proposed and are being used, which carry out the matching process continuously while the hearing aid is being worn and thus take into account the influence of the head on the reception of acoustic signals. The parameters in these algorithms are essentially two factors, an amplitude factor and a phase offset between the two microphone signals. Factors such as these also are used on a frequency-band specific basis. The algorithms on average, that is to say for diffuse interference sound, achieve matching that is as good as possible.
German PS 199 27 278 discloses a method for matching microphone of a hearing aid, as well as a hearing aid for representing the method. In this case, a hearing aid with a number of microphones which are connected to one another in order to produce a directional characteristic are ensonified in a suitable measurement area, and the directional characteristic is recorded, while the hearing aid is being worn. Filter parameters that are obtained from this can be supplied to configurable filters, which are connected downstream from the microphones, and the desired ideal directional characteristic can thus be approximated taking into account the individual characteristics when the hearing aid is being worn. The method makes it possible to produce filter parameters for amplitude and/or phase response matching of the signals, which are recorded by the microphones, in order to optimize the directional characteristic of the microphones.